Magnus (Divided Loyalties)
According to one account, in his original incarnation, Magnus, the Time Lord who would later become the War Chief attended the Prydonian Academy as part of the Deca. Other members included Theta Sigma, later the Doctor, and Koschei, later the Master, (PROSE: Divided Loyalties) in contrast to accounts suggesting the War Chief and the Master were incarnations of the same Time Lord. (PROSE: Doctor Who and the Doomsday Weapon, etc.)
Biography
According to a Time Lord history book written after the Last Great Time War, like all children of Gallifrey, the War Chief was taken from his family at the age of eight for the initiation rite in the Drylands. Staring into the Untempered Schism as part of the Time Lord ritual, he was reportedly "driven mad" by what he saw in the Schism. (PROSE: A Brief History of Time Lords)
However, at the Academy, he was considered an excellent student. In the student group known as the Deca, Magnus was noted for his "commanding personality" which meant "most of them found it difficult to argue with him". Koschei was extremely jealous of Magnus's ability to "just speak, click his fingers, or whatever, and [make the others] follow", once remarking, "One day I must find out how to do that" to Vansell. Despite her cold exterior, Magnus carried on an affair with Ushas, to which Mortimus, to Magnus's amusement, was oblivious, having been harshly rejected by Ushas himself and come to the conclusion that she wasn't interested in dating boys at all.
During his student years, Magnus heard "rumours" about a species of "Aliens" who had come to Gallifrey demanding to be given time travel that they could put to use in War Games, and been expelled from the planet with a threat of temporal erasure if they ever returned. He later mentioned it to his friends, and Jelpax confirmed the story, having read about it in a record book in Coordinator Azmael's library.
After Millennia and Rallon were lost to the Toymaker during an ill-fated escapade, Magnus escaped blame, and "got himself assigned to the scientific research department for the rest of his time at the Academy". He was the only member of the Deca to attend the ceremony whereby which Theta Sigma was expelled from the Academy, having taken the fall for the other two's disappearance. Subsequently, clapping him and Jelpax on the shoulders, the Doctor pointed them out to Vansell as true friends who had been loyal to him, and to whom, in turn, he would always be loyal, come what may. (PROSE: Divided Loyalties)
Fate
By the time his thirst for glory began to put him at odds with a First Doctor who had yet to leave Gallifrey, Magnus was no longer in his first incarnation. (COMIC: Flashback) He subsequently "fled his homeworld" in search of the Aliens he had read about, (PROSE: Divided Loyalties) eventually finding them and becoming the War Chief of their final War Games. (TV: The War Games)
Legacy
A history of Gallifrey written after its destruction in the War in Heaven concurred that "Magnus" had been a member of the Deca, separately from Koschei. (PROSE: Gallifrey: A Rough Guide) A Time Lord history book written after the Last Great Time War also listed "the War Chief" as a separate Time Lord from the Master and recalled each eight-year-old Time Tot's experience with the Untempered Schism separately. (PROSE: A Brief History of Time Lords)
Behind the scenes
In a deleted line from the AUDIO: Neverland script, the Eighth Doctor mentions both Magnus and a certain "Koschei" when reminiscing about the Deca.
